The present invention relates to internal bone fracture fixation devices. In one application, the present invention relates to bone fracture fixation devices and methods adapted for fixation of femoral neck and other proximal femoral fractures.
The femur, otherwise known as the thigh bone, generally comprises an elongate shaft extending from the hip to the knee. The proximal end of the shaft includes a head, a neck, a greater trochanter and a lesser trochanter. The head of the femur fits into the acetabular cup of the hip bone to form a ball and socket joint at the hip. The distal end of the femur includes a medial condyle and a lateral condyle. The condyles engage an upper end of the tibia to form the knee joint. Overall, the femur is the longest and strongest bone in the skeleton. However, portions of the femur are extremely susceptible to fracturing.
Pertrochanteric fractures among geriatric patients are the most frequent in connection with those of the region of the neck of the bone. The advanced age and the pathologies which are encountered in these patients make a timely stabilization of skeletal injuries necessary in order to reduce to a minimum the bed confinement and the rehabilitation times. Preferably, devices and procedures are utilized which minimize complications brought about by the so-called immobilization syndrome, which may be lethal for patients in delicate metabolical circumstances. It is also preferable to reduce to a minimum blood losses related to surgical intervention. At the same time, the syntheses means utilized must be stable in order to allow the patient to very timely assume a seated position and, two or three days following the intervention, to reassume an erect posture with progressive bearing of weight.
Internal fixation of femoral fractures in general is one of the most common orthopedic surgical procedures. Fractures of the femur occur in both the proximal portion of the femur and the distal portion of the femur. Fractures of the proximal portion of the femur (hip fractures) are generally classified as femoral neck fractures, intertrochanteric fractures and subtrochanteric fractures. Fractures of the distal portion of the femur (knee fractures) are referred to as supracondylar fractures. Supracondylar fractures generally extend vertically between the condyles at the lower end of the femur to separate the distal portion of the femur into two main bone fragments. A fracture line may be further comminuted to create a plurality of smaller bone fragments. Fractures of the femur which extend into the neck of the bone are generally more difficult to treat than fractures restricted to the shaft of the femur.
Operative treatment of the fractures requires that the fractures be internally fixed and possibly compressed. Fractures of the neck, head or trochanters of the femur have been treated with a variety of compression screw assemblies which include generally a compressionplate having a barrel member, a lag screw and a compressing screw. The compression plate is secured to the exterior of the femur and the barrel member is inserted into a predrilled hole in the direction of the femoral head. The lag screw which has a threaded end and a smooth portion is inserted through the barrel member so that it extends across the break and into the femoral head. The threaded portion engages the femoral head. The compressing screw connects the lag screw to the plate. By adjusting the tension of the compressing screw the compression (reduction) of the fracture can be adjusted.
A variety of elongated implants (nail, screw, pin, etc.) have been developed, which are adapted to be positioned along the longitudinal axis of the femoral neck with a leading (distal) end portion in the femoral head so as to stabilize a fracture of the femoral neck. The elongated implant may be implanted by itself or connected to another implant such as a side plate or intramedullary rod. The leading end portion of the, implant typically includes means to positively grip the femoral head bone (external threads, expanding arms, etc.), but the inclusion of such gripping means can introduce several significant problems. First, implants with sharp edges on the leading end portion, such as the externally threaded implants, exhibit a tendency to migrate proximally towards the hip joint bearing surface after implantation. This can occur when the proximal cortical bone has insufficient integrity to resist distal movement of the screw head. Such proximal migration under physiological loading, which is also referred to as femoral head cut-out, can lead to significant damage to the adjacent hip joint. Also, the externally threaded implants can generate large stress concentrations in the bone during implantation which can lead to stripping of the threads formed in the bone and thus a weakened grip. The movable arms of known expanding arm devices are usually free at one end and attached at the other end to the main body of the leading end portion of the implant. As a result, all fatigue loading is concentrated at the attached ends of the arms and undesirably large bending moments are realized at the points of attachment. In addition, conventional threaded implants generally exhibit insufficient holding power under tension, such that the threads can be stripped out of the femoral head either by overtightening during the implantation procedure or during post operative loading by the patient""s weight.
Thus, notwithstanding the variety of efforts in the prior art, there remains a need for a femoral neck fixation device with improved locking force within the femoral head, which resists migration and rotation, and which can be easily and rapidly deployed within the femur.
There is provided in accordance with one aspect of the present invention, a method of securing a first bone fragment to a second bone fragment. The method comprises the steps of drilling a bore through the first bone fragment in the direction of the second bone fragment, and advancing a fixation device through the bore. At least a first portion of the fixation device is rotated to secure the fixation device to the second fragment, and a second portion of the fixation device is axially advanced to engage the first fragment.
In one application of the method, the second bone fragment comprises the head of a femur. Alternatively, the second bone fragment comprises the tibia, the fibula, or the femur. The first bone fragment may alternatively comprise a condyle.
The method may additionally comprise the step of positioning a plate adjacent the first bone fragment and advancing the fixation device through the plate.
In accordance with another aspect of the present invention, there is provided a femoral neck fracture fixation device. The device comprises an elongated body, having a proximal end and a distal end. A helical distal anchor is provided on the distal end. A first retention structure is provided on the body, proximal to the distal anchor, and a proximal anchor surface is moveably carried by the body. The proximal anchor surface is moveable in the distal direction with respect to the body, and the retention structure resists proximal movement of the proximal anchor surface with respect to the body.
In one embodiment, the first retention structure comprises an annular structure such as one or more flanges or threads. The proximal anchor surface may be carried by a tubular sleeve, for axially moveably receiving the elongate body. A second retention structure is preferably provided on the interior of the tubular sleeve for cooperating with the first retention structure on the body.
In accordance with a further aspect of the present invention, there is provided a bone fracture fixation device. The fixation device comprises an elongate body having a proximal end and a distal end. A cancellous bone anchor is carried by the distal end. A proximal anchor is axially moveably carried on the body, and a complementary surface structure is in, between the body and the proximal anchor to permit advancing the proximal anchor in the distal direction to tighten the fixation device but resist axial proximal movement of the proximal anchor.
In accordance with another aspect of the present invention, there is provided a method of treating a femoral fracture. The method comprises the steps of drilling a bore distally into the femur in the direction of a fracture, and advancing a fixation device into the bore. The fixation device is rotated to engage bone distal to the fracture, and a proximal anchor is advanced distally along the fixation device to compress the fracture.
Preferably, the drilling step comprises drilling the bore along an axis which extends through the femoral neck and in the direction of the head of the femur. In one embodiment, the advancing a proximal anchor step comprises axially advancing the proximal anchor without rotating the proximal anchor with respect to the fixation device. The femoral fracture may be a femoral neck fracture, an intertrochanteric fracture or a subtrochanteric fracture.
Further features and advantages of the present invention will become apparent to those of skill in the art in view of the detailed description of preferred embodiments which follows, when considered together with the attached drawings and claims.